When Department of Oceanography & Coastal
Sciences (DOCS) graduate student Nicole Smith finishes her
master’s thesis, she will have accomplished something
truly unique—the most thorough study of the feeding
ecology of the paddlefish ever conducted in the United States.
This prospect makes Louisiana Department of Wildlife and Fisheries
(LDWF) biologist Bobby Reed very happy.
“I’m glad it was done in Louisiana,” said
Reed, nicknamed “Mr. Paddlefish” by Smith’s
advisor, DOCS Associate Professor Richard Condrey.
Smith’s study, carried out in collaboration with LDWF,
began at the suggestion of Reed. Smith and Condrey consulted
Reed on a Sea Grant classroom project that involved raising
paddlefish in captivity, and at the end of that project Smith
wanted to continue working with paddlefish. They asked Reed
what further research he would like to see done on the paddlefish.
Reed recognized Smith’s interest as “one of those
opportunities that come along” to fill in a gap in the
scientific knowledge about the paddlefish, a true river and
estuarine fish inhabiting the Mississippi River, adjacent
gulf coast drainages, and upper estuaries. He asked her to
undertake a feeding ecology study in conjunction with LDWF
sampling in Mermentau. Reed began studying the American paddlefish,
Polyodon spathula, in Louisiana in 1986, the year it was placed
on the state’s protected list. Prior to that, very little
information on paddlefish in the state could be found.
For the past 12 years, the Mississippi Interstate Cooperative
Resource Association (MICRA), a consortium of the game and
fish agencies in 28 states organized “to improve interjurisdictional
river resource management in the Mississippi River Basin,”
has studied the American paddlefish. Because the fish is migratory,
sometimes moving hundreds of miles within a few weeks, it
needs to be managed on a partnership basis.
In the early 1990s MICRA formed the Paddlefish Committee with
a primary objective of managing sustained fishing of the paddlefish
in states where it is numerous enough to be fished and to
sustain the species where it is protected. Bobby Reed is in
his third year as chairman of this committee.
According to Reed, paddlefish propagated and released as fingerlings
8–16 inches long are implanted with a coded wire tag
(CWT) that is so small, 1 ml long and 1/3 mm in diameter,
that it can be found only with a $10,000 handheld detector
comparable to those used in airports. Because the CWT is so
small and unobtrusive it has no effect on the fish, which
allows unbiased studies to be conducted. Everyone in the 22
MICRA states involved in the study uses the same CWT and collects
the same information, so they have been able to conduct a
very comprehensive study resulting in a database with information
on 2.2 million individual fish. It is the largest study undertaken
for any kind of freshwater fish in the United States. The
only thing comparable is the study on the anadromous Pacific
salmon, which uses detectors in the ladders the fish jump
to get to their spawning grounds.
Because of the MICRA project, a lot of information about the
paddlefish is available now. But there is still much to learn—such
as their feeding ecology. That’s where Nicole Smith
comes in.
Smith’s research consists of two parts: one is a detailed
analysis of the gut contents over seasonal and developmental
stages in each sex, and the other examines how the body changes
morphometrically as it grows. To accomplish this study Smith
accompanied LDWF personnel as they sampled paddlefish in the
Mermentau River basin. Her permits with Wildlife and Fisheries
and LSU allowed her to collect up to 15 paddlefish per month.
The earliest North American fossil record of the paddlefish
is from the Upper Cretaceous. Its closest living relative
is the Chinese paddlefish. And the only group of fish in North
America that even resembles the paddlefish is the sturgeon.
What those two fish have in common is very palatable eggs,
or roe, which is sold as caviar.
Sixteenth century explorers of the Mississippi River reported
seeing the paddlefish, which were once abundant. Because of
over-harvesting and habitat loss from dam construction and
watershed alteration, paddlefish populations were already
in decline when the United States placed an embargo against
Iranian caviar in the 1980s. Paddlefish roe demand soared,
and poachers took their toll—and Louisiana was no exception.
Paddlefish, which are very sensitive to the anoxic water conditions
produced by storms, can be hard hit by hurricanes. “In
Hurricane Andrew,” said Smith, “100,000 adult
paddlefish were wiped out in the Atchafalaya Basin.”
But, their only natural predators, of adults anyway, are alligators
and humans. The paddlefish, although long-lived, take a long
time to mature sexually. Males can spawn at four to nine years;
females spawn at ten to twelve years. They don’t necessarily
spawn every year. If the water temperature isn’t right,
acceptable substrate isn’t available, or the river isn’t
on a rise, the females just reabsorb their eggs and wait until
the next spawning season.
Paddlefish are easy to recognize because of their very distinctive
“nose,” known as a rostrum. The rostrum has electroreceptors
that can detect groups of plankton and even plankton appendage
movement. With the rostrum evidently playing a major role
in detection of prey, it is curious, Smith notes, that paddlefish
that don’t have their rostrums can still feed so well.
She found a number of paddlefish with damaged or missing rostrums
that still had full stomachs. Tubercules, recesses or sacs
found on the skin over the paddlefish’s whole body,
may contain a variety of sensory receptors that respond to
a number of stimuli and help the fish locate prey.
In addition to getting quantitative estimates of the fullness
of the paddlefish stomachs, Smith also analyzed the contents.
“I’ve found a number of things,” Smith said.
“I’ve found copepods, cladocerans, nematodes,
ostracods, amphipods, larval fish, and tentatively identified
chain-forming diatoms. The contents mainly consist of copepods
and cladocerans. With the help of Dr. John Fleeger, I have
found that the nematodes are parasitic.”
Condrey is especially intrigued by the diatoms, which were
found in very high numbers in some paddlefish sampled in May.
They are not mentioned in any literature about paddlefish.
He would like to pursue further studies to determine if the
paddlefish are selectively preying on the algae, or if they
are just ingesting them coincidentally.
Smith also found that egg masses in females could account
for up to 30 percent of their body weight, compared with only
4 percent for testes in males. She said that the mass of eggs
could take up most of the body cavity.
The LDWF is considering cutting back on the 50-100,000 paddlefish
fingerlings they raise for release each year at the Booker
Fowler Fish Hatchery in Woodworth, Louisiana. They have stopped
sampling in the Mermentau River and are now sampling in the
Calcasieu River. “They know the numbers are good in
Mermentau,” said Smith, “so they’re moving
to another area. So, the numbers of paddlefish are improving
in Louisiana. And I know they have no intention of opening
the season again, except maybe on a by-catch basis.”
In the conservation efforts to help the recovery of the paddlefish,
Smith’s research on their feeding ecology will fill
an important gap in the knowledge about this intriguing, ancient
species. And this study is likely to be just the first: when
asked what she plans to do after she graduates, Smith replied,
“I want to work with paddlefish.”
[Smith would like to acknowledge a grant from Sea Grant and
the help of Bobby Reed, Eric Shanks, Paul Smith (all with
LDWF), Mark Benfield, Hongsheng Bi, John Fleeger, Guerry Holm,
Sean Keenan, Charles Sasser, and Malinda Sutor. Photographs
were provided by Nicole Smith and more are available in the
photo gallery at scenews.lsu.edu]
Websites
of interest: |
|
|
www.nanfa.org/ac/2000sring1.pdf Interesting article
in North American Native Fishes Association newsletter
titled “Horned Serpents, Leaf Dogs, and Spoonbill
Cats: 500 Years of Paddlefish Ponderings in North
America.”
http://www.tpwd.state.tx.us/expltx/eft/nasa/species/paddlefish.htm
Texas Parks & Wildlife
http://www.cnr.vt.edu/efish/families/polyodontidae.html
The Virtual Aquarium of Virginia Tech
http://www.earthwave.org/paddlefish.htm Award-winning
documentary “The Paddlefish: An American Treasure”
available
http://www.ag.auburn.edu/fisheries/peak/paddlefish
Restoration of paddlefish in Alabama
http://www.usdoj.gov:80/enrd/caviarFINAL.htm
http://www.usdoj.gov:80/opa/pr/2002/January/02_enrd_052.htm
Two cases of smuggling and use of American Paddlefish
roe as “counterfeit caviar.”
http://wwwaux.cerc.cr.usgs.gov/MICRA/pscomm.htm MICRA
paddlefish and sturgeon commission
http://www.ohioriverfdn.org/conservation/paddlefish.html
|
